Thermosetting phenolic resin adhesives may be prepared by reacting phenols, such as phenol or cresol, with aldehydes, such as formaldehyde or acetaldehyde, in a strongly alkaline medium. The phenolic adhesives are generally not compatible with ordinary acidic hardeners, and therefore require a higher curing temperature and a longer curing time in comparison with other thermosetting resin adhesives made from urea resins or melamine-urea co-condensed resins. Such higher curing temperatures and longer curing periods for phenolic adhesives inevitably lead to lower production yields of adhered products such as plywood. As a result, the commercial applications of phenolic resin adhesives have been significantly limited despite their excellent properties such as good bonding strength and water resistance.
Although various methods have been proposed for shortening the curing time of phenolic resin adhesives, these methods have not been generally successful in that the cost of formulating the adhesive with the various additives employed has been significant.
Accordingly, it is a principal object of this invention to provide a relatively inexpensive method for preparing a phenolic resin adhesive having enhanced bonding strength, water resistance, and curing time.